1. Field Of This Invention
This invention relates to new types of polyolefin copolymers prepared from gaseous monomers and more specifically to ethylene-propylene copolymers.
2. Prior Art
A wide variety of polymers made from one or more alpha-olefins are in extensive use for a wide range of applications. For example, several grades of polyethylene are commercially available. These are low density polyethylene (LDPE) produced by a high pressure reaction and high density polyethylene (HDPE) produced by a low pressure fluid-bed, or slurry, transition metal catalyzed reaction. In addition, there are commercially produced a series of copolymers for example, the ethylene-ethyl acrylate (EEA) series. All of these resins have applications as insulating covers in the wire and cable area among others. They are flexible but are deficient in higher temperature properties. There has been, therefore, considerable interest in the preparation of LDPE-type products having higher melting points and which are based on polypropylene.
Ethylene-propylene copolymers are well known. Block copolymers of these two alpha-olefins are also well known. Commercially available polypropylene resins are either homopolymers or of the AB type propylene-ethylene copolymers. These AB block copolymers, although having improved impact strength over polypropylene are still high modulus plastics (100,000 psi). A recent polymer, now being commercialized does have a lower modulus (about 15,000 psi) but is deficient in tensile strength and elongation. In addition, these materials appear to be graft copolymers of propylene and ethylene-propylene rubber (EPR) and thus require an additional mixing step in their preparation, are chemically ill defined and contain appreciable amounts of homopolymer which detract from their mechanical properties.
The alpha-olefinic polymers of this invention have significantly different and improved mechanical properties over existing commercial copolymers, blends of polypropylene and EPR as well as LDPE and EEA.
Certain process techniques disclosed in U.S. Pat. No. 3,804,881, and to some extent disclosed in U.S. Pat. No. 3,839,293, may be employed in the practice of this invention. However, the polymers of this invention are not disclosed in either of these patents. The polymers disclosed and claimed herein are new and possess unexpected beneficial properties not heretofore attained for polymers made from the same monomers. Attention is also drawn to U.S. Pat. Nos. 3,427,287; 3,448,173 and 3,562,235 and British Pat. No. 1,292,226. None of these latter patents disclose the polymers of this invention or techniques for making them. No other more pertinent prior art is known.